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Breast Cancer Res Treat. 1998 Jul;50(2):175-84.

Use of oral contraceptives and risk of breast cancer in young women.

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  • 1Department of Preventive Medicine, University of Southern California/Norris Comprehensive Cancer Center, Los Angeles 90033-0800, USA. gursin@hsc.usc.edu

Abstract

Many studies have shown that oral contraceptive (OC) use increases a young woman's risk of breast cancer, although some studies suggest that the risk may be limited to recent use. The objective of this study was to determine what particular aspects of OC use could be important for breast cancer development at an early age in the cohort of women who had the opportunity to use OCs all of their reproductive life. The cases were first diagnosed with breast cancer at age 40 or younger between 1983 and 1988, and identified by the Los Angeles County Cancer Surveillance Program. Control subjects were individually matched to participating cases on birth date (within 36 months), race (white), parity (nulliparous versus parous), and neighborhood of residence. Detailed OC histories were obtained during in-person interviews with subjects. In general the risk estimates were small, and not statistically significant. Compared to no use, having used OCs for 12 years or more was associated with a modest non-significant elevated breast cancer risk with an odds ratio (OR) of 1.4 (95% confidence interval (CI) = 0.8-2.4). Long-term (12 years or more) users of high-dose estrogen pills had a non-significant 60% higher breast cancer risk than never users (CI = 0.9-3.2). Early use was associated with slightly higher ORs among young women (age < or =35), and among parous women. Recent use was associated with somewhat higher ORs among parous women and women above age 36. Analyses by stage, body weight, and family history yielded similar results. This study is consistent with a modest effect of early OC use on breast cancer risk in young women.

PIP:

The relationship of breast cancer risk in young women to particular patterns of oral contraceptive (OC) use was investigated in a case-control study conducted in Los Angeles County, California (US), in 1983-89. Enrolled as cases were 744 White women 40 years or younger at the time of breast cancer diagnosis who were located through a population-based cancer registry. One community control was matched to each of these cases on birth date, race, parity, and neighborhood of residence. OCs had been used by 83.3% of breast cancer cases and 84.4% of controls; 68.6% of cases and 69.3% of controls had used OCs for 12 months or more. In general, the results revealed only a modest effect of early OC use on breast cancer risk in young women. Compared to never use, OC use for 12 or more years was associated with a small, nonsignificant elevated breast cancer risk (odds ratio (OR), 1.40; 95% confidence interval (CI), 0.81-2.40). Women who used high-dose estrogen formulations for 12 years or more had a nonsignificant increased risk compared with nonusers (OR, 1.64; 95% CI, 0.85-3.18). Among women below age 35 years at diagnosis, compared with never users, women who had used OCs for 1 year or more before the age of 18 years were at almost twice the risk of developing breast cancer (OR, 1.97; 95% CI, 0.90-4.32). Among women over age 35 years at diagnosis, compared with never users, those who had used OCs for 3 or more years during the past 5 years were at a 2.54-fold increased risk (95% CI, 0.94-6.88). Analyses by cancer stage, body weight, and family history failed to detect any significant effects.

PMID:
9822222
[PubMed - indexed for MEDLINE]
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